1. Field Of The Invention
This invention relates to the addition, during the printing process, of ink to ribbons being used in an impact printer, such as a typewriter or dot matrix printer, and is specifically applicable to the field of inked ribbon cassettes.
2. Description Of Prior Art
A century of experience has proved inked ribbons are a superior method of supplying the ink to impact printers. This technique, however, has two major limitations which have been the subject of many inventions: (1) The quantity of ink the ribbon can hold is small, so the ribbon must be frequently discarded or re-inked at considerable cost; and, (2) The amount of ink transferred by the impact depends on the amount of ink on the ribbon, so even the small ink load on a ribbon cannot be completely used by multiple passes, before the quality of the impact printing declines.
Considerable prior art in the printing industry has alleviated these limitations by using a mechanism comprising an ink reservoir, a feeder, and a roller to apply ink to the ribbon and thereby extend the inked ribbon lifetime. Since the proliferation of high speed dot matrix printers using throw-away, inked ribbon, cassettes, the utility of reducing the life cycle costs of cassettes has motivated similar inventions adapted to cassettes. Each invention uses one or more of the components (reservoir, feeder, and roller) in a unique combination to add ink to a ribbon.
Such prior art is exemplified by patents by Castro (U.S. Pat. No. 4,390,294), Ogan (U.S. Pat. No. 4,364,678), and Okamura (U.S. Pat. No. 4,449,838). Castro provides a device, separate from the printer and cassette, for adding ink to the ribbon. This alternate to simply replacing the entire cassette, or re-loading the cassette with an inked ribbon, can reduce ribbon costs by a factor of ten, but requires a messy operation, interuption of the printing process, and no relief from the decline, with use, of print quality.
Ogan provides a felt pad ink reservoir, inside the cassette, in continuous contact with the ribbon. This eliminates the messy operation, but, because of the limited space available inside a standard cassette, adds only a small fraction to ribbon lifetime. In addition, if the pad is heavily loaded with ink to maximize the lifetime improvement, the pad, in continuous contact with the stationary ribbon when the printer is not in operation, will locally saturate the ribbon, and produce unacceptably non-uniform print.
Okamura provides a larger reservoir, and an additional transfer roller (restricted by claims to . . . turned by contact friction with the ribbon . . . ) to control the flow rate from the reservoir to the ribbon. Successive step increases in roller-reservoir pressure increase the flow as the reservoir is depleted. In addition, the roller acts as a demand valve, feeding ink to the ribbon only when the ribbon is moving, to avoid local over-inking and allowing maximum ink storage in the reservoir by permitting saturation of the reservoir. Both the reservoir, and the roller with its springs to control ink flow, are located inside the cassette. The space required by the reservoir and the roller is obtained at the expense of space normally filled, in a standard cassette, with ink-containing ribbon, so, any increase in lifetime is restricted to the excess of ink capacity of the reservoir over the ink capacity of a slightly larger volume of ribbon. This invention cannot be adapted to existing cassettes.